مَا كُلُّ مَا يَتَمَنَّى الْمَرْءُ يُدْرِكُهُ
A person does not obtain everything he desires.
This does not mean that none of a person's wishes are fulfilled. It rejects the stronger proposition that every desired thing is obtained; some desires may still be achieved.
The continuation of the verse pictures winds and ships to reinforce the mismatch between wishes and events. The example neatly illustrates the scope of mā over a construction headed by kull.