The Purpose of Tefillah
Although we may not always see immediate results from our prayers, we should remain hopeful. According to our sages, there are instances where a certain number of prayers are necessary before they are answered from Heaven.
However, there is another important aspect of tefillah that is often overlooked, and taking it into consideration might lead to swifter outcomes.
One of the reasons why Hashem created the system of tefillah is to establish and maintain a connection between Man and his Creator. By engaging in regular prayer, people remain conscious of Hashem's presence and involvement in their lives. Therefore, the ongoing nature of one's needs and prayers serves to foster an enduring connection with Hashem.
Circumventing the Delay
This is why sometimes prayers are not immediately answered by Hashem, as this encourages people to sustain their connection with Him, a connection which would otherwise weaken over time. But for someone who undertakes to continue talking to Hashem even after his wish is granted, there is no reason for the yeshu'ah to be hindered anymore.
The Arvei Nachal writes that this method was adopted by Dovid Hamelech, who implored (תהלים פו ג) Be - חָנֵּנִי ה' כִּי אֵלֶיךָ אֶקְרָא כָּל־הַיּוֹם - Be gracious unto me, Hashem, for unto You do I call all day. The Arvei Nachal elucidates that with this, Dovid expressed his determination to continue calling upon Hashem regardless of the immediate fulfilment of his wishes, thereby enabling his desires to be fulfilled promptly.
(ערבי נחל וארא דרוש א ד"ה יוצא מכלל)