Dependencies are both comforting and terribly dangerous for a small business.
If all or most of your work is coming from a single customer you are setting yourself up for a painful episode.
Best to minimize these situations, even if the temptation to work for that one huge customer that always pays on time is tremendous.
What will happen is this: as you work for that one customer all your other customers are finding other ways to satisfy your needs. And then one day your ‘One Big Customer’ (OBC) will fall over or decide that you are out of fashion and you will find that your whole network has atrophied.
Or, worse, they go under and leave you with a huge unpaid bill (because of the trust factor you figured it was ok if they didn’t pay for a few weeks).
So, best to avoid these depencies. As a rule you should not get more than 25% of your annual turnover from the same source, go beyond that at your peril.
There are other dependencies besides the dependency on a single customer, it might be that you are dependent on a single third party that you hire for every job, again, you have to spread the risk and work on having multiple parties that can fill these roles.
One day someone will cross the street without looking and now you have two problems in stead of just one.