"Man does not tire of praying for good," meaning: he does not become bored. "But if evil touches him, then he is despairing, hopeless." To the polytheist, the good is the worldly life, health within it, and prosperity. "And if evil touches him," in the form of loss of wealth or an unexpected illness, he does not hope for reward in the Hereafter, nor does he hope to return to the prosperity he was previously in.
﴿لَا يَسْأَمُ الإِنْسَانُ مِنْ دُعَاءِ الْخَيْر﴾ أَي: لَا يملُّ ﴿وَإِن مَّسَّهُ الشَّرُّ فَيَئُوسٌ قَنُوطٌ﴾ فالخير عِنْد الْمُشرك: الدُّنْيَا وَالصِّحَّة فِيهَا والرخاء ﴿وَإِنْ مَسَّهُ الشَّرُّ﴾ فِي ذهَاب مالٍ، أَو مرضٍ لم تكن لَهُ حِسْبة , وَلم يرجُ ثَوابًا فِي الْآخِرَة , وَلَا أَن يرجع إِلَى مَا كَانَ فِيهِ من الرخَاء