Question

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

Answer 1

Because in Spain, most people don't go to sleep very early. Many people in Spain sleep in the wee hours of the morning, mañana. So it will rarely happen because they either forget or don't think about it till the next day

Answer 2

When a Spaniard says they will complete a task "mañana", it rarely happens the next day because "mañana" is a usual expression to defer activities, there are many sayings with this like "Today I don't guarantee, maybe tomorrow", surely in posters, but if the person arrives the next day, the poster still there and that day the place doesn't guarantee neither.

Step-by-step explanation:

The procrastination is a problem for many people of Spain and Latin America, that's the reason why they have created sayings and other forms to joke themselves about it.