Question

If a spaniard says they will complete a task"manana" whywill it rarely happen the next day

Answer 1

In Spanish culture, there is almost never a reason to hurry to get something done. That’s why if you go to Spain, public transportation will normally be late, guests expect to show up late, and services aren’t done at the time they are supposed to.

Answer 2

Answer: This says that when a "spaniard" says that he will do something tomorrow, most likely he/she will not do it.

First, you can not assume that only because someone mother tongue is the Spanish, is most likely that the person is a procastiner, it may be true that the Spanish culture is a little bit more "flexible" than other ones in the subject, but there is no an actual answer to the given question.