The Most Important Word?

Following the Tidy and Late - topics - I wonder what others feel is the most important WORD in the dictionary?  My feeling is that SORRY rates as very important. 

Recently I have had issues with nPower over a new meter they say I haven't got - and so the meter readings don't tally as they might.  Not once have they apologised for wasting my time or calling me a liar.  Similar issues with Anglian Water but they have apologised - whoever trains their switchboard people does a great job.  And today - I had a rather abrasive  person on the phone arranging a hospital appoint at the hospital - She declared she had nothing till Tuesday 11th of July!  So I laughed and said I don't think so - surely it would have better if she had said "sorry - silly me - I mean the 21st?" or words to that effect?  But she barked out the time etc.  I know we all have bad days but a little humour helps those days along in my opinion.  I have been a telephonist in a business - and I would have been sacked if I had spoken like this one. 

I nominate - Sorry, Please and Thank you probably in that order.