Johnson didn't give Parliament much of a chance either. He *knew* that they would block him on No Deal if he were insistent upon it. He decided, presumably with the backing of advisers, to meet that threat by trying to shut Parliament out of the debate -- rather than the sensible thing, which would have been to work with them. He cannot have been surprised when Parliament pushed back, and indeed was almost certainly counting on it. Although he clearly underestimated the scale, and miscalculated the likelihood of opposition parties supporting an election on his timetable.
On the subject of No Deal, the entire approach of "you have to be prepared to walk away" is flawed for another reason. In a negotiation, if you want to persuade your opposite party to make concessions, then they have to believe that you'll accept a deal one those concessions have been made. Otherwise, why waste the point in making them?
If you want to reach a deal with someone, you have to convince them that you will shake hands under at least some circumstances.