YouCantPushaPieceOfString is LeaderShip advice.

For instance, most programmers are naturally motivated to do a good job. They want to produce quality software that the customer wants on time. Generally speaking, programmers don't have a problem putting in extra effort to a project when needed. The pride of craftsmanship and the thrill of creating motivate them.

However, the customer wants the software yesterday. The customer also wishes foo would baz a little more, fap would be expanded to include fips, moops would be able to be treated as mips -- bells and whistles ad nauseum. The programmer also thinks it would be cool if foos could baz and fips could bip, even though the customer didn't ask for it. And to complicate matters, bipping the foo took a lot longer than the programmer thought.

As a result, the project ends up where most software projects do: not enough time to do all the things wanted.

Enter PointyHairedBoss. He doesn't notice that all the people involved do not share a common vision for the functionality. He doesn't notice the unrealistic time expectations of the customer (or marketing department or programmer). These can't possibly be the source of the problem; the real problem is that ProgrammersAreLazy! PointyHairedBoss thinks the solution to the schedule crisis is to get the time-wasting programmers to work a lot of overtime. And since programmers are trying to avoid programming, they need incentives like promised bonuses at the end of the project. LawOfDiminishingReturns? Bah -- humbug! Eighty-hour weeks are twice as good for the product as FortyHourWeek''''''s!

Guaranteed to sap the internal motivation right out of programmers.
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You can't push a piece of string comes from physics 101 force diagrams involving ropes and weights and pullies. The student is asked to calculate the forces for various parts of the system. If the student calculates that one of the forces involves pushing (rather than pulling) on a rope, the student knows (hopefully) that they have screwed up their calculations somewhere. "You can't push a string" is sometimes described as the "zeroeth law of force diagrams".

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I saw a vagrant pulling a chain along the ground the other day, so I stopped and asked him, "Hey mate, why are you pulling that chain?". He replied, "Have you ever tried pushin' one?"
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Let's say there is an instance where you need to push a string. It is possible. Here's how:
soak the part of the string you need to push with water. Cool the segment to well below the freezing point of water. You can then push that segment. 

''The problem is then that you're not pushing string, you're pushing a cylinder of frozen water that happens to surround some string? It might or might not solve your original problem, but it doesn't disprove the original assertion.''

{True, and it's a demonstration of the fact that no matter how obviously metaphorical or allegorical you are, there's always some crank at the back of the room who interprets it literally. Of course, maybe he was being '''so''' profoundly metaphorical that it shot off the screen to the right, wrapped around, and came back out the left '''looking''' literal.}

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On a low-enough friction surface and with stiff enough string, it's possible. Both literally and metaphorically.

''Put some Viagra on it.''
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Sometimes the boss knows what's going on, but does it this way for another reason that's not apparent to subordinates, perhaps to get more staff. Things are often not what they seem.
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HowLongIsaPieceOfString?