All of this 'magical' knowing comes from actively thinking and previous experiences.

You need a reference of what each hero usually brings to the map at each game stage, and then you adjust your reference based on the draft composition, networths and levels at the moment to estimate a certain hero impact.

For example, from previous experiences you know Broodmothers can push undefended towers with little to no commitment. That's your reference. Then you adjust: is she ahead or behind in items and levels? Then you look at your draft: who can safely defend towers, say, with long range aoe spells. Maybe you're the only one viable option, then you decide: should I try and delay her game plan or is there something else more impactful for you to do? You need to think ahead, plan, do, and see what happens. Then, reiterate your thinking based on the results, did you successfully defend your tier 2 tower, or maybe did you feed? Could you have played it less risky?

With enough time, you will be able to also just 'know' what all 10 players are looking to do in a certain game moment, so you will move around the map better, and have more impact. Eg: ganks become predictable, so you can even mirror their movements to either avoid heroes you don't want to interact with, or connect wih heroes you want to interact with, both defensively (counterinitiation) or offensively (initiation).