All good answers here except for letting your lunch draft for you.
It somewhat depends on the player I think too.
Some players you may see as values compared to their draft position, but they may not be players that you think you must have on your team.
To give an example I think Lamar Jackson is going to be a difference making player in fantasy in 2019. I think his ADP is lower than it should be but I want to make sure I am the person drafting him. Therefore I am willing to reach ahead of ADP as ZWK suggests.
I also think Mike Gesicki is a player with more upside than the other 2018 rookie TE. However I am not so high on him that I would draft him ahead of ADP the way I would Jackson. I do not really care if I miss out on drafting him. So I won't reach, but I would be happy to take him at ADP.
need2know makes a good point to not use too many of your picks on players who you see as underdrafted. If you reach ahead of ADP on a lot of your picks, then you are not getting value out of taking players who you think the consensus are too low on.
jvdesigns makes a good point about your draft position dictating when you may need to reach on a player if you really want to have them. If you are drafting at the ends for example and a lot of picks between your pick and your next pick(s) then you have to be thinking rounds ahead a bit more than being able to let the draft come to you when drafting in the middle. If you see a QB run about to happen for example, you may want to take the best QB a round or two higher than the ADP just because you can't be sure a good one will still be available to you if you wait until your picks at the next turn.
I am usually not ;locked in to any specific players as ones that I think I must have. I like a lot of players and I see many players as all being in the same tier, so if I cannot get player X because they were drafted before me, not a big deal as I will just draft player Y or Z instead. Lamar Jackson would be an example of a player that I can't draft another player like him, so he gets priority from me and I will reach for him to make sure I get him, because there isn't any other player that I see having the same upside as Jackson.
Where this kind of thing comes into play for me is when I can trade during the draft. If I have 8 players in the same tier at my pick for example, then I am fine with trading down 7 spots as I am then sure I will still get one of those 8. Sure I might like one of those 8 more than the rest, but if I can still get the last guy of the tier and add value in another pick by trading down, then I do that. The only exception to this would be if I think the player is a unique talent, such as my Lamar Jackson example. Then I won't trade down if he is there, as I don't want to risk not getting him.
I recall doing several drafts and also mock drafts in 2016 where I thought Jay Ajayi was really under valued. In early drafts I was taking him way ahead of his ADP just based on my projections. I think the earliest I drafted him was the 4th round. I think many considered this a reach at the time and based on ADP it was, but he still provided value to me at that draft position. Each draft I participated in I kept drafting him a little lower than the one before. The signing of Arian Foster greatly helped this cause. As it turns out I was happy that I had him in almost every league I was in that year, but he provided a lot more value to my teams that took him later than the ones where I selected him early. There is an opportunity cost of reaching on a player even if that player had the most value for the draft position you used on him, you still could have taken another player not as valuable at ADP and also added the player with the highest value later in the draft.