Can you please explain what this rule means in simple words?

State Code Art. 2 1423.Cause defined;detrimentalreliance

A party may be obligated by apromisewhen he knew or should have known that the promise would induce the other party to rely on it to hisdetrimentand the other party was reasonable in so relying. Recovery may be limited to the expenses incurred or the damages suffered as a result of the promisee'srelianceon the promise. Relianceon a gratuitouspromisemade without required formalities is not reasonable.(Note, Doyle's is the promisee)