It's all mind over matters. Your brain controls everything. I can't get hard if I don't have chemistry with the girl and I can't get hard without LFK or DFK for FS. Some girls I really like and have chemistry with, I don't need no pills. I also have a hard time cumming with just a HJ at semi legit spas without LFK. So I always pick and choose who I play with.
One thing though..sometimes some girls play dirty trick if they don't want to do FS with you. They cock block you by tightening their vagina muscle. I came across one a while back while I was in Bangkok. The girl was complaining too big and tightening her muscle whenever I made attempt to enter her V. I distracted her mind with an insect on the ceiling and slid it in. She was fine after that.