What is the reason that the answer to prayer does not last long, and what is the wisdom behind that?

Supplication is entirely good and is one of the greatest means of achieving what is sought. So, do not despair; rather, increase in it, for the servant is answered as long as he does not hasten, and Allah loves those who are persistent in supplication. Your supplication will not go in vain: either it will be answered, or Allah will avert evil from you because of it, or He will store it for you on the Day of Resurrection. Increase your supplications with certainty of being answered, gather your heart, seek out the times of response, and take hold of its means. The response to supplication may be withheld due to shortcomings in thanking for blessings, or persistence in disobedience. Blame yourself and do not blame your Lord, for the servant is afflicted by his own shortcomings. Adhere to obedience to Allah, for Allah is Wise and All-Knowing, placing things in their proper places.