This topic is going to example tactics and strategy from the perspective of jrpgs, but you Tactics is the decisions you make in combat, while strategy is the decisions you make out of combat.

Tactics

Tactics are the decisions you make DURING combat. For example, what spell to cast, what persona to equip, when to defend, when to wait in ambush. To win on a tactical level is obvious, you won the battle, or beat the stage. good job. To lose, is more nuanced. You very well may be failing in some tactical way, you could be not exploiting the hitstun of an arte you know as much as you could be, or positioning poorly and getting destroyed.

Strategy

Aside from grinding, many players failing in basic and embarrassing tactical ways, are also in majority several magnitudes more a complete failure in the strategic layer. Where tactics are the actions DURING battle, strategy is the actions OUTSIDE of it. What weapons to buy, what skills to learn, to pay attention to text, read menus carefully, and realize powerful combinations. Most players, are horrible at deciding who gets what. They foolishly equip some wind resistance shoes to their healer, not realizing exactly how terrible going before the boss is for the character with the teams revive spell. Or teach their tank a powerful attack, despite that when anything actually challenging comes along, a tank/support mix would be better.

If your losing in a game, try taking a serious consideration, to if your active performance (Tactics) are the reason, or if your missing something in the bigger picture (Strategy). Heres a tip: if you think games in the shin megami tensai, super robot wars, paper mario, etrian odyssey, final fantasy, dragon quest, octopath, golden sun, or zelda series are "hard", then your probably garbage at both of these. Calm down, and go train, meaning retrying those fights with difference tactics and equipment strategies until you win. Don't grind, get smarter.