Buying too much modells, then never finishing painting. Painting a modell or squad too long (my 9 TS modells are not done even yet, and I paint them since a month). Converting nearly every army, wich I owned (9. army this time on the table), consuming too much time, never get done with them, getting bored, and selling them (I still have 3 armies this time Black Templars, Eldar and Chaos SM).
Always writing hard lists, using nice tactics, but then, the dice is against me, as I attack a squad, witch I can beat (SM assault marines, 8 modells +vet searg with power fist+ chaplain with PW attacking 10 modells of eldar guardians +1 warlock), and ending beeing massacred (only the chaplain lived at the end of turn)... Oh, and watch as somebody uses my list, and my tactics, and butchering everything on the table, what does not belong to him... This is the hardest, and it makes me cry!
Buying too many armies, then throwing them out before finishing for another... Getting beeted too much time.