Everyday . . .

A new business is born that requires your product or service.
A business wants to grow and they need your help.
A sales rep goes M.I.A. leaving an orphaned account for the taking.
A business moves into your area finding it easier to deal with a local company.
A new buyer joins the company looking to make a name for themselves.
That old buyer who used to tell you "No!" may have left.
A vendor drops the ball creating an opening for you.
A vendor gets complacent creating opportunity for you.
A rep fails to offer an idea that you have that could impact your prospect's business.
A buyer just doesn't like their rep.
A buyer hates the buying process with their vendor.
A buyer wants to deal with someone who isn't just about the commission check.
A buyer feels like they are over paying for what they are getting.
A rep misses a deadline
A rep fails to communicate properly giving you an opening.
A company needs the benefits of your offering to help them streamline their process.
A buyer wishes they could find a vendor that would "get it right the first time".
A referral from an existing account is there for the taking
A "low ball" company can't sustain quality
A sales rep gets caught in a lie to a customer losing credibility
A vendor implements some stupid, non customer friendly policy
A vendor raises their price making the buyer reevaluate the situation.

Source: Paul Castain, Sales Playbook, Play #8.