Beginners defend too much. A white three you have already capped is SLEEPING: it can never make an open four, only a rush four with a single, predictable five-point — you may answer that four when it actually comes, so blocking early spends a whole move on a threat that is not yet alive. Now two white threes sit on the board — one sleeping (you capped it), one wide awake. Spend your move on the live one.
Finish this step to move on.