[bell-cot]

With competent defenders, "the fast way" has a high failure rate. And even if successful, a high body count.

Or, if you're referring to gunpowder/cannon tactics - those are the reason for medieval-style fortifications falling out of favor, 1500 CE-ish.

[IAmBroom]

Nope, I meant pre-gunpowder.

But as always, money can break any castle wall. But lobbing putrefied meat into wells, waiting out their stores, and so forth work.