[jegutman]

I'm a national master chess player and I think the opposite. In middle games heuristics are more important because even the final positions in your calculations will often still be very dynamic so you need some tools to be able to evaluate these positions you've never seen before. In endgames the same thing may happen, but the confidence around my evaluation will generally be much higher.

[jlg23]

Yes, heuristics are a very good guideline and I am grateful to have learned those at a very early age (that's how you were introduced to chess in the GDR).

I too apply them but my point is, in mid-game I'm much more free to ignore them than in openings or end-games in which I usually let my forearm do the thinking.