It means you don't understand how he works (I had a similar case with Wukong and Yasuo before I started drilling the hell out of the two).
To give an example, way back while learning Yasuo, I always tend to dash right up to the enemy laner, smack them around, get out, and win trades for my first few games. After a while however, the message that carried on was "Yasuo wins trades, you should get into fights all the time!". Long story short, first game goes great, second game okayish, third and onwards is a downhill struggle of feeding hard. I eventually noticed that in the first game of a day I play with Yasuo, I play passive enough that I always have his shield before I would think of engaging, and I also learned the trick to abusing midlane as a melee champ (Cooldowns), and from that point onwards, my game with Yasuo was far more consistent.
Not a Lucian player so I can't give advice, but try to figure out why Lucian works in those first few games and what mistakes you make based on that. Do you happen to win trades a lot and like me get cocky and start making bad decisions? Are you a passive player who waits for a late game spike, which is perfect against some ADCs but isn't that great against a heavy hyper carry? Really, it's the little things that are incomprehensible if you don't understand your champion well enough, but the key to drilling a certain champion is figuring out what these things are.