Things will go wrong...
After working on events for many years, there is one piece of advise that I give to any client:
Three things will go wrong.
These things may be tiny or massive, you can never know, but you must accept that they will be there. I have found that if you can accept this fact then those glitches are easier to handle. Also, what is massive to one Bride, for example, will be small to another but its all about how you handle them.
Obviously, having a Wedding Planner or Event Consultant on board, like me, they can take the strain and figure out what to do about it. If you don't have this in place, have you tried to consider the possibilities and asked someone else to help if something should happen? Choose someone who will not only stay calm but can take control in a compassionate and constructive way.
To handle something happening you must be in the right frame of mind from the start. I have had experience in helping my client to be relaxed and open throughout planning and on the day so that these things don't influence the event. They concentrate on what is important and calmly deal with the issue, not letting it take over.
It might be that the issue has a dramatic effect on the day so the people around you are the most influential factors for this. For example, for one wedding I was coordinating the Brides Great Aunt had a heart attack. With the help of the guests, the Bride and Groom didn't find out what had happened until two days later! That's team work and keeping calm!
I hope this little snippet of advise helps make you aware and handle anything that comes your way!