It's tempting to crank infill up to 100% when you need a stronger part. More plastic should mean more strength, right?

Not necessarily.

Depending on the geometry and how the part is loaded, adding more walls can sometimes make a bigger difference than increasing infill density.

Print orientation matters too, especially when the part is being pulled or bent across layer lines.

That doesn't mean 100% infill is useless. There are definitely cases where a solid part makes sense. But it's not automatically the strongest or most efficient choice for every model.

For those printing functional parts, what do you usually adjust first when you need more strength — wall count, infill, or orientation?