I remember when I first played Discworld 2 back in late 1990-s, and didn't have any internet access, I got stuck at a certain puzzle for about a month, finally giving up and uninstalling the game.
A year later I reinstalled it, and this time breezed through that point, bemused by how I hadn't been able to see the fairly obvious solution the first time around. And then I got stuck again, near the very end. It took me a few more years and a guide to learn that I needed to talk to a certain NPC that had a random, and not very high at that, chance of appearing at a certain location every time I visited it - and finally finish the game.
These days I just don't have that kind of time or patience. So if I can't solve a puzzle for more than 2-3 hours - it's guide time. Usually it turns out that I was thinking in the right direction, but forgot to do that one little arbitrary thing that change the logic of the solution but was deemed necessary by the designer.