How many testimonies we have not heard from people who came to the ways of the Lord asking for confirmation; If you are God and you do this or that I accept you. The Lord is not manipulable yet sometimes He responds to challenges, trials or fleeces. Because he knows the hearts of men and knows who have the desire to trust him.

The first one who made use of the fleece in the Bible was Gideon, Judges 6:37 “behold I will put a fleece of wool in the era; and if the dew were only on the fleece, the whole other land being dry, then I will understand that you will save Israel by my hand, as I have said "
It is obvious that Gideon did not feel confident about the great task that the Lord had assigned him. Instead of acting in faith, he introduced his famous fleece, not to discover God's will but to gain complete certainty of success. Repeatedly in scripture, the Lord calls us to be faithful. Genuine trust in God means that we follow him wherever he shows us, without worrying about the results. Job said "even if He will kill me, I will wait on Him."
We must take each step out of faith, not out of fear, doubt, or anxiety. Although at some point we have done like Gideon, we have had to turn to God in prayer to look for a sign that gives us encouragement in need.