Let’s look at a subtle difference between demasiado in Spanish and too in English.
As you know, too is used in English to compare the current situation with an ideal one. It’s too difficult means that is would be better if it were less difficult. He’s too poor means that it would be better if he were not so poor. Even you’re too kind suggests — perhaps insincerely — that it would be better if you weren’t so kind. In each case, reality is evaluated against an ideal world.
The case with demasiado is a bit different. Although demasiado can often be translated as too, sometimes it simply means very — without the implication of an evaluation. In the examples below, demasiado is synonymous with muy.
- Es demasiado informal. It’s very informal (and that’s a good thing). Here, too is not a possible translation.
- Mi pelo es negro y lo uso, generalmente, demasiado corto. I have black hair, which I usually keep very short. This doesn’t mean too short. (a personal ad)
- La verdad es que me cansé demasiado. I’m wiped out from carrying something so heavy. There was nothing in the situation that would allow us to ask Too tired to do what? This was simply a neutral comment meaning really tired. (television dialogue)
Context will determine which meaning is intended.
Adjective or adverb?
Keep in mind that demasiado can be an adjective or an adverb. This explains why demasiado agrees with its head in hay demasiadas personas, where it is an adjective, but not in son demasadiado feas, where it is an adverb.