I've lived near an ocean most of my life—in Southern California, the Visayan region of the Philippines, and now in NE Florida. I'm familiar with the power of currents and tides.

Solid footing, secure moorings, and anchors are needed to prevent a person or a vessel from drifting off. Even where currents are gentle, if a boat isn't tied securely to its mooring it will drift away.

Rivers can be treacherous and even lakes when unexpected squalls kick up. Jesus' disciples knew this from experience. They also learned to not rely upon their own expertise and experience when it came to matters of faith.