Too uses

Too 

its means more than enough its always use in good sense its means excess then i expected

Too+ infinitive 

with too if we use infinitive verb (to +verb) then it sense in negative
for an example

He is too weak to walk . 

here , we use in sentence too with to weak  , its infinitive and here its mean he is weak as weak that he can not walk .

too is used in excess
like

you are too week in mathematics. 

here you are weak in mathematics much than you should not