Do not take it personally when someone in your work life does not reply to you today, they are just busy.
When you are trying to reach someone in your work life today and you do not get an answer, do not panic. This could be a new client or a colleague you are working on something with. Whoever it is, they are busy and your email or letter has not been seen yet. They are not ignoring you so do not take it personally, just try again and they will reply when they can.