The principle of the lesser of two evils is derived from Homer’s Odyssey. In the story Odysseus must sail through the Straits of Messina to get home. On either side of the straight are two monsters, Scylla, a six headed monster who chucks rocks at boats and Charybdis, a giant whirlpool.
Odysseus decides to sail past Scylla, losing six of his crew but avoiding Charybdis, who would have sucked down the ship killing everyone. The point is that Odysseus has to sail though the straight and therefore has to decide which of the two evils will cause the least harm.
The lesser of two evils is a principle that states when forced to choose between two seemingly immoral options, you adult-up and chose the less immoral of the two. You don’t use it as an excuse to sit on your arse doing nothing and whinging about how they’re all as bad as each other. That’s how the greater of two evils usually wins.