Affordability
Eve tip of the day: Don't fly what you can't afford to lose.
This is maybe the second most fundamental rule in eve, the first being 'never trust anyone'. And higher importance of the third rule: never fly through Rancer. https://zkillboard.com/character/798282716/losses/system/30002718/ for reference. 😄
Eve constantly has mechanisms to push you towards 'shipping up'. a lot of 'oh you could do this if you just get into this ship'. But getting into that ship might be a few weeks to a few months. And then training those associated skills are a few months minimum usually, but years for some others. The key is to not get into a ship too early.
For example, an Eagle, which I'm sure everyone is very eager to get into. Yes, you can get into it in only a month and a half, but training t2 weapons hardeners and other skills is a LOT longer. and we only SRP things that are properly fit, so if it's missing modules or has a 'fitting' module, you might get denied. In fact, you can get denied for just being a mango, which I have NEVER had happen to me. cough https://zkillboard.com/kill/86705527/
So, you have to constantly have the idea in your head, what am I flying to replace this ship. Maybe you have to fly something smaller afterwards. Maybe you have to move down in ratting ships to afford it. Maybe you have to wait for SRP because you can't afford to replace it yourself. But you need to consider the fact that every ship you ever fly in eve is dead the moment you undock.
This message brought to you by the guy who lost 4 eris yesterday. 😄
https://forums.eveonline.com/t/8-golden-rules-for-eve-online/3973 I went looking for a source on this concept and this is pretty solid.
from sugar crush: you can maybe add that 'remember that there is now a Plex Vault, so you never, ever, ever have to fly plex around in your ship...'.