I have trouble moving from 4 to 5 too, yes. I just chalk it up to "its tough," and thats that. Most of that stuff happens with 4* girls, the same ones I get in my box occasionally when doing the 1000-seed gacha, and I give it a whirl again. I end up wasting ~2500 gold when it happens, but yeah. I don't have the numbers or any studies to back it up, but you're not alone on the lack of success. I've been playing videogames (well before this type of game) for many years, so delayed gratification and leveling up people for a long time is nothing new to me at all. Dragon Warrior on NES will prepare you for anything.