Be accountable
Common Behaviour
One of the most common traits I see among people is a lack of personal accountability. I'm guessing you know what the word accountable means, it's a synonym for responsible, and in this context, it refers to people not taking any responsibility for their faults or actions. In a lot of cases, this involves blaming other people.
Of course, I'm no saint either. We're all sinners and I've certainly been guilty of this behaviour myself, but this attitude is incredibly unhelpful. Here's why.
Dating Scenario
A young guy finds a girl attractive and wants to know her. So he goes up and talks to her. To which she politely responds with "sorry, but you're not really my type". Later on, the guy speaks to his friends about his rejection and says "well I didn't really like her anyway, girls only like guys who are tall, rich, and mistreat them".
In this scenario, the guy wasn't rejected because the girl already has a boyfriend, he was rejected because she isn't interested in him. Although we don't know the exact reason why he's not her type, it's obviously something on his behalf. Whether it's something he has control over or not, the problem is he's blaming her for where he lacks and stereotypes other girls because one girl didn't like him.
Since his ego has been hurt, he insists he wasn't that interested in her to avoid feeling humiliated. Of course, if he didn't like her, why would he talk to her?
Blaming others is unhelpful
The problem with blaming other people for your problems is that you don't bother trying to solve them. It's both narcissistic (because you deny the fact you're part of the problem) and pessimistic (because you're admitting defeat over something you have the potential to solve).
If the guy humbles himself and realises "if I'm getting rejected a lot, maybe there's something wrong with me, not them", then he can work on aspects of himself that possibly turn girls away. Maybe it's not his height or his wealth. Maybe it's his physique, or something as simple as his hygiene or manners.
Hold yourself accountable even if it's not your fault
I'm not saying you should take responsibility for something you haven't done, that's unfair and unreasonable. What I mean is you should think about what you could've done instead of just pointing the finger.
Let's suppose you are late to an event because of traffic. While it is an annoying situation and not entirely your fault, you could've arrived on time if you left earlier.