Simultaneously managing attack and defense I am an amateur chess player. I have the knowledge of pawn structure, development of the pieces and control of the center in the opening. After that my midgame rationale is attacking the weak pieces, and if I am under an attack, focus on defense. This has failed to work among much stronger opponents of late. How would I change my rationale so that I can manage defense and attack at the same time?
Defense isn't something that one does; it is not a tactic. Instead, defense happens when one has ceded the initiative to the opponent. One spends moves patching holes versus attacking the opponent's weaknesses.

(Of course at some point "tactics" and "retaining the initiative" blur. Some fine attacking moves also defend, and some defensive moves free other pieces to attack. It can be a maelstrom when it comes to specifics.)

So consider reading on tempo and initiative.