"Humankind cannot gain anything without first giving something in return. To obtain, something of equal value must be lost. That is alchemy's first law of
Equivalent Exchange."

Edward Elric, Full Metal Alchemist / Full Metal Alchemist: Brotherhood

Let it be said that in life, there is no such thing as action without consequences. I know that, and you probably do too. Whatever you gain, something must be given in return. Much as we would like to hope it to be true, that we could get something for nothing. But that never happens. And when we (mistakenly) assume that to be so, there's always payback. And most of the time, and it comes more often than not with interest (even more so when we believe / hope that there will not be consequences).And its never, ever cheap. That's why they say payback's a bitch, fate (or karma / a divine being or whatever you believe in) can be cruel. Occassionally with a sense of twisted humour to rub it in. Remember, there's always a catch.

Doing things for people with this philosphy in mind may not always portray you in a good light (i.e. mercenary, calculative), but that's the truth isn't it? because nobody does something for nothing (and the 'excuse' of being altruistic doesn't hold water with me. People say they get that warm, fuzzy feeling for helping someone. I think that's your payback right there). Either there is some vested interest, or something of value you believe you can get in return.

This is why freelancers (contrary to their title) should never work for free, why social workers can burn out after years on the job provided they don't have good work-life balance / recharging (and if they do have that recharging / balance, then the system gives up something in exchange right? Thus proving the philosophy to be right).

If I dare say it without causing anyone undue offence, the same can be said of religion. Taking my own Christian belief as an example, despite what is said, "unconditional" love of God (and eternal life that comes through believing) is not as "unconditional" as you think. Because to receive that, you first need to believe, and once you do, you take on a whole new set of values / social norms. While it may be argued that sooner or later this eventually becomes second nature to you (the living out of the values / social norms / philosophy put into practice), there are undoubtedly instances where your faith will be tested, to varying degrees and in different circumstances. Don't tell me that isn't your payback. To gain something, you need to give up something in return.

Let this be said about "equivalent" exchange. It is not up to your valuation of what you get in return / give up (more often than not, you're often aggreived by the fact that you get considerably less in return for what you've given up). But who are you to say that your valuation is right? How do you measure the sacrifices and their rewards (especially those that are more... intangible)? I guess the reason why you do that is to get something, you need to give something of value to yourself. And because of the nature of what you give up, that's why it seems disproportionate You feel what you give up is highly valuable to you (while this may not be true for others). For you to feel that it has been sacrificed, it has to hurt. That's what the nature of sacrifice is.

Something for nothing doesn't exist. Newton's 3rd law (for every action there is an equal and oppostie reaction) embodies equivalent exchange (in some sense), and its something that people who are less naive are aware of - There's No Such Thing As A Free Lunch.