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At the start of the game, a number from 1 to 255 is generated, which determines the hero's skill tree. The tree is called a tree because you can develop along different branches. However, the tree as a whole remains unchanged throughout the game.
Sometimes, you can identify the tree. For example, if a rare skill for the hero appears at early levels, then there are likely only 1-2 such trees. Someone gave the example that Craig has exactly one tree with diplomacy on the 2nd level (SoD). That is, seeing diplomacy on the 2nd level, you can continue to develop wisely (if there are records for this tree).
Similarly, in WoG, Brogh has a "lol-tree" where all the necessary skills are given in a row (3 speed, offense, water, tactics), but the scout advances on the 17th level, I think. I myself have encountered this, and I have seen it in reports; there is only one such tree. Here, you need to realize in time that you have entered this tree and break it by refusing something.
Also, for Brogh, there is a terrible tree with tactics on the 2nd level, where if you take it, you won't get anything useful; there is artillery further on, wisdom, fire, etc.