The power of dua is so much stronger than we can imagine. After the death of Abu Talib (ضي الله عنه) and Khadijah (ضي الله عنها), the Prophet (صَلّى االلهُ عَلَيْهِ وسَلَّم) decided to go preach Islam somewhere else besides Mecca. He traveled to the city of Taif, where he was ridiculed, physically harmed, and rejected by the rulers and inhabitants.
The Prophet (صَلّى االلهُ عَلَيْهِ وسَلَّم) was very distressed, but he asked the Almighty for help in the dua below and Allah subhanah wa talla provided help.
To You, my Lord, I complain of my weakness, lack of support and the humiliation I am made to receive. Most Compassionate and Merciful! You are the Lord of the weak, and you are my Lord. To whom do You leave me? To a distant person who receives me with hostility? Or to an enemy You have given power over me? As long as you are not displeased with me, I do not care what I face. I would, however, be much happier with Your mercy. I seek refuge in the light of Your face by which all darkness is dispelled and both this life and the life to come are put in their right course against incurring your wrath or being the subject of your anger. To You I submit, until I earn Your pleasure. Everything is powerless without your support.
Aisha (ضي الله عنها) reported about the incident at Taif:
أَنَّ عَائِشَةَ ـ رضى الله عنها ـ زَوْجَ النَّبِيِّ صلى الله عليه وسلم حَدَّثَتْهُ أَنَّهَا قَالَتْ لِلنَّبِيِّ صلى الله عليه وسلم هَلْ أَتَى عَلَيْكَ يَوْمٌ كَانَ أَشَدَّ مِنْ يَوْمِ أُحُدٍ قَالَ " لَقَدْ لَقِيتُ مِنْ قَوْمِكِ مَا لَقِيتُ، وَكَانَ أَشَدُّ مَا لَقِيتُ مِنْهُمْ يَوْمَ الْعَقَبَةِ، إِذْ عَرَضْتُ نَفْسِي عَلَى ابْنِ عَبْدِ يَالِيلَ بْنِ عَبْدِ كُلاَلٍ، فَلَمْ يُجِبْنِي إِلَى مَا أَرَدْتُ، فَانْطَلَقْتُ وَأَنَا مَهْمُومٌ عَلَى وَجْهِي، فَلَمْ أَسْتَفِقْ إِلاَّ وَأَنَا بِقَرْنِ الثَّعَالِبِ، فَرَفَعْتُ رَأْسِي، فَإِذَا أَنَا بِسَحَابَةٍ قَدْ أَظَلَّتْنِي، فَنَظَرْتُ فَإِذَا فِيهَا جِبْرِيلُ فَنَادَانِي فَقَالَ إِنَّ اللَّهَ قَدْ سَمِعَ قَوْلَ قَوْمِكَ لَكَ وَمَا رَدُّوا عَلَيْكَ، وَقَدْ بَعَثَ إِلَيْكَ مَلَكَ الْجِبَالِ لِتَأْمُرَهُ بِمَا شِئْتَ فِيهِمْ، فَنَادَانِي مَلَكُ الْجِبَالِ، فَسَلَّمَ عَلَىَّ ثُمَّ قَالَ يَا مُحَمَّدُ، فَقَالَ ذَلِكَ فِيمَا شِئْتَ، إِنْ شِئْتَ أَنْ أُطْبِقَ عَلَيْهِمِ الأَخْشَبَيْنِ، فَقَالَ النَّبِيُّ صلى الله عليه وسلم بَلْ أَرْجُو أَنْ يُخْرِجَ اللَّهُ مِنْ أَصْلاَبِهِمْ مَنْ يَعْبُدُ اللَّهَ وَحْدَهُ لاَ يُشْرِكُ بِهِ شَيْئًا ".
That she asked the Prophet (ﷺ) , 'Have you encountered a day harder than the day of the battle) of Uhud?" The Prophet (ﷺ) replied, "Your tribes have troubled me a lot, and the worse trouble was the trouble on the day of 'Aqaba when I presented myself to Ibn `Abd-Yalail bin `Abd-Kulal and he did not respond to my demand. So I departed, overwhelmed with excessive sorrow, and proceeded on, and could not relax till I found myself at Qarnath-Tha-alib where I lifted my head towards the sky to see a cloud shading me unexpectedly. I looked up and saw Gabriel in it. He called me saying, 'Allah has heard your people's saying to you, and what they have replied back to you, Allah has sent the Angel of the Mountains to you so that you may order him to do whatever you wish to these people.' The Angel of the Mountains called and greeted me, and then said, "O Muhammad! Order what you wish. If you like, I will let Al-Akh-Shabain (i.e. two mountains) fall on them." The Prophet (ﷺ) said, "No but I hope that Allah will let them beget children who will worship Allah Alone, and will worship None besides Him."
Don't ever doubt the strength and power that a simple dua can have on your life. Allah subhanah wa talla is always there to answer your dua.