The term burn your boat in crude terms means to take an irreversible decision.
Here are some interesting articles I want to share on the same.
http://ezinearticles.com/?Burn-The-Boats---Finding-Passion-in-Your-Life&id=545736...beautifully said and the para about about being afraid of "them" is exactly I keep saying! Liberating to read it!
"Until one is committed, there is hesitancy, the chance to draw back, always ineffectiveness. Concerning all acts of initiative and creation, there is one elementary truth the ignorance of which kills countless ideas and splendid plans: that the moment one definitely commits oneself, and then providence moves too. All sorts of things occur to help one that would never otherwise have occurred. A whole stream of events issues from the decision, raising in one's favor all manner of unforeseen incidents, meetings and material assistance which no man could have dreamed would have come his way. Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now." - Johann Wolfgang von Goethe .
Very true. Gandhiji also said something thing similar in his book The story of my experiments with truth :
"The freedom and joy that came to me after taking the vow had never been experienced before. Before the vow, I had been open to being overcome by temptation at any moment. Now the vow was a shield against the temptation."