Keeping differences in mind...
What they have done in the past they will still do in the future...
Do you have that colleague who is always late for a meeting? You want to change their behaviour, because you hate the impact on your world. The first step is to accept that it is impossible to change some-one's behaviour unless they want to change it themselves.
We need to accept that everyone is different and accommodate differences rather than fighting against them and only really causing pain to ourselves. If we don't recognise and accept the differences we will be disappointed by the reality as we have had unrealistic expectation about their behaviour.
We have to accept that what they have done in the past they will do in the future? so if they have always been late they will be late going forward.
If you analyse your disappointment you will see that you are disappointed by something they have never done. You are only disappointed by your unrealistic expectation.
Blow away the myth that people want to be treated the way you want to be treated. As an example, I hate being late and arrive everywhere quite early. I would like to be prompted on timing and if running late would love someone to tell me. My husband is late all the time and would not be happy to be prompted on timing, in fact the prompts often have the reverse effect and make him slow down and ultimately he gets even later.
Compassion is key in accepting differences and accepting the behaviour you have seen is what you are going to see again. Therefore allowing extra time or creating fake times that accommodate the lateness.
Be compassionate with yourself rather than beating yourself up. I work very near the wire on most projects, it is unrealistic to think that I will work in another way. I can look at past projects and know that is the way and accept it, far better than to be angry with an unrealistic way to behave that I have never done.
