My personal meta-cynical view is that politics is all about relationships: nobody gets anything done using their own power alone, and nobody has enough broad and direct influence to even try. Getting anything done requires aligning a lot of people, each holding either a direct ability to implement a part of the solution, or the connection and ability to influence someone that does. This includes not just outward-facing projects and decisions, but also politicians' own careers - whether you get in, and where you end up, is more to your colleagues than it is to you.
As a result, the whole system strongly selects for people best able to navigate that complex web of relationship. Which means it selects against people with goals they're not willing to compromise on.
This is why, I think, in modern (democratic) countries you can't really achieve anything specific by becoming a politician. If you come in with a concrete and inflexible goal (like, to reuse the example, making the government fund free food for children), you'll likely just wash out or get sidelined by your own colleagues: if you're not willing to help with whatever others need from you, even when it means compromising your principles or going against your initial goals, then nobody else will be willing to help you with your schemes. The rules of thumb thus are:
- If you see someone going into politics to achieve a specific goal, you can assume they'll fail and the goal will not be achieved;
- If you want the politicians to do something, you need to go about it indirectly, exploiting the incentives of the entire system - for example, as alleged upthread with the food for children, by setting things up so the government will lose face / influential politicians will lose public support if they don't implement the very thing you want them to.
- Everything that's actually being achieved is achieved in a roundabout way, because the limiting factor isn't any politician's ethics, understanding, or budget - the limiting factor is the ability to align enough politicians and administrative workers to make something happen.