I'll define this properly first. 
There is a difference between reason and excuse.
To me, an excuse is something which used to console yourself. 
Example, I can't lose weight because I can't exercise because my back hurts. 
This is an excuse, cos there are other options and other exercises which you can do to lose weight.
Or, I got a car because my wife is working in the far corner of the country.
This is also an excuse, cos she can still take public transport, just that she needs to wake up earlier.

Whereas, to me, a reason, is a valid explanation of something. 
Example, I was late for work today because I was stuck inside the MRT when it broke down.
It can't be helped and there's no other