Though the path be straight and narrow, there is no promise that path will not be bumpy or broken. Throughout the Proverbs, there is strong "pathway" imagery to communicate where our hearts should stay and where we should avoid. Often the path we are told to stick to is that which is straight and narrow, because that is the pathway God lays before us. It is the path which leads to Him. It is the path which leads to life.
We are to avoid the wandering path set before us by enemies and various temptations. This is the wandering pathway which leads to nowhere. It is the wandering pathway which also leads our hearts to death.
While the straight and narrow path may be broken and bumpy, it is still straight. We can be assured that continuing straight will lead us to life, hope, and ultimately, Christ.
While the wandering path may be smoothly paved with enticement, comfort, and ease, it is still aimless and leads to death.
We may choose the rocky road that is straight to the top, or we could choose the paved switchbacks that never end but in death.