In a tetrahedral frame, like this one shown in blue and red, there is no one side that is more important than any other side. The colors are used solely as a visual cue, to help viewers immediately recognize its shape and structure. Instead of regarding one particular side as always and necessarily being the base and/or foundation, it's more useful and helpful to notice that, if this type of frame is pushed or blown hard enough to knock it over, it becomes exactly the same shape, all over again. That is one of its strengths, assets, and resources, which embodies adaptability, responsiveness, etc. Those are good things, not bad things.
And, please notice that if ANY of the four triangular panels which form an enclosed tetrahedral frame is removed, then that will directly breach and violate the closure, security, and protection which can be provided by a complete enclosure. All three sloping walls, and the base as well, must be present, for proper strength, stability, protection, etc.  
In a similar way, the DELTA component,
in the lower right corner of this square
depiction, is NOT a leftover, an unwanted
hanger-on, or a mere annoyance. Instead,
it can . . . it should . . . and if done right,
it MUST . . . be regarded as the crucial
fourth element, which is absolutely essential to enabling the complete structure to work properly, if it is going to be stable and successful. It must NOT be merely tolerated, grudgingly and resentfully. Instead, if a relationship (or family, or company, or partnership) is going to last, as a stable, happy, fulfilling, and productive entity, then all four of the essential components need to be present.
In mathematics, the Greek letter delta -- ∆ -- is used to represent a change in some quantity. A "difference" of some sort, between where something "started", and where it "ended up" or "arrived at".
Similarly, the delta in the lower right corner of the tetrahedral square represents the DIFFERENCE between the male and the female who are thinking about getting married, or forming a business partnership, or whatever (as described on the previous page).
 
As a basic statement of business principles, nearly any "partnership" will work better -- it will be more productive, more profitable, more stable and durable, etc. -- if each of the partners brings, to the table, something which the other partner(s) generally does not have, or cannot do well, or does not enjoy doing. A serious question is, if two people do the exact same things in the exact same way, then why do they really NEED each other? That is not how the best partnerships work. Instead, the classic pattern, for good business partnerships, arises when: (i) one of the partners has more of a creative, artistic, innovative, think-outside-the-box temperament and talent, while (ii) the other partner is better at handling details, budgets, annoying paperwork, and financial discipline.
To make the same point on a different level, my wife and I have enjoyed (despite problems, challenges, struggles, etc)  a good relationship, for more than 30 years, precisely BECAUSE we did different things, all day long, at work. She became a talented, successful, and powerful executive at a major company, with a  number of white-collar workers reporting to her, in a complex management hierarchy. So, each evening when she came home, I would simply ask, "How did your day go?", and that would almost always lead to an hour or so of interesting, intelligent conversation -- which is exactly the sort of thing that can help sustain an interesting and intelligent relationship, for years and even decades.
And, as another example of how the DIFFERENCE between two people can be an essential and much-appreciated part of a relationship -- when she would eventually circle around to asking me, "And how did YOUR day go?" -- well, I was under no obligation to answer HER question in the same way she had answered MINE. And, I didn't. Her nature, her identity, and her skill set, are all tied up in being a really, really good manager -- at being able to work well with people, at being able to spot anomalies, at being able to home in on real problems without getting tripped up by unimportant ones, and at being able to make people feel and understand that they still were (and had to be) on the same team, even if someone had made a bad mistake.
 
Since she is so well-adapted and skilled at being a manager, if I had given her any kind of opening or opportunity to reach in, grab a "managerial hold" on my problems, and start telling me how I should handle them, that is exactly what she would have done. And that is NOT what I wanted, when it came to me, as a patent attorney, working with my inventor-clients. So, I would simply say, in response to 98% of her nightly questions, "My day was fine. I worked for this particular guy, on the such-and-such invention." That was all the answer I chose to give her, and within a reasonably short time, that was all she came to expect.
The important point is, that was okay with her. It was okay for me to answer her question in one way, even though she chose to answer the exact same question, from me, in a totally different way. Because each of us having enough freedom, support, and approval to doing what we did, in whatever way worked best for EACH of us, is what enabled the system and structure to work best, for BOTH of us.
 
As I look back on our careers and our life together, I see that as a classic and even perfect example of how the DIFFERENCE between two people -- i.e., the DELTA part of their relationship -- is an absolutely crucial and essential FOURTH component, which enables the other three components to work well, if and when they are assembled and integrated into a single functioning system (such as a family).
Okay, then . . . if you're still awake and willing, and have time, let's go on to the NEXT point . . .