Weakness and Fear made Peter Deny Jesus Christ.
“Meanwhile, Peter was still standing in the courtyard by the fire. And one of the guards standing there said to him, “Aren’t you one of his disciples? I know you are!” Peter swore and said, “I am not his disciple!” But one of the servants of the high priest, a relative to the man whose ear Peter had cut off, looked at him and said, “Wait! Didn’t I see you out there in the garden with Jesus?” Then Peter denied it the third time and said, “No!”—and at that very same moment, a rooster crowed nearby.”
John 18:25-27(TPT)
Jesus had earlier warned Peter about the impending temptation, and boldly Peter assured Him it would not happen. 
At Gethsemane, Peter was supposed to pray and be stronger spiritually, but he was very, very sleepy, so when the tempter came, there was no spiritual stamina. 
At that point, he was weak spiritually.
Having learned his lessons, Peter later wrote, “Be careful—watch out for attacks from Satan, your great enemy. He prowls around like a hungry, roaring lion, looking for some victim to tear apart.” 1 Peter 5:8.
You need to pray and prevail in prayer to avoid falling into temptation.
It’s not by mere “positive confession.” 
Fear was the other reason that made Peter fall.
Peter feared Jesus would die, and they could kill him that night too. 
The world hated Jesus and so they would hate you too. 
It’s been said that there are 365 “Fear not’s” in the Bible, one “Fear not” for every day of the year. 
Most times, our fears do not come correctly, as we had worriedly feared.  
God told Joshua to be bold and courageous. “In the same way I was with Moses, I’ll be with you. I won’t give up on you; I won’t leave you. Strength! Courage!” Joshua 1:8 (MSG)
“Simon, Simon, Satan has asked to have you, to sift you like wheat, but I have pleaded in prayer for you that your faith should not completely fail. So when you have repented and turned to me again, strengthen and build up the faith of your brothers.” 
Luke 22:31-32
Today don’t allow weakness and Fear to make you stumble. Peter did turn around, so also you can.
Pray and Prevail in Prayers. Have Strength and courage