  It is argued that there is a fundamental momentum cutoff in heavy-to-light
transitions, which is caused by possible Cherenkov gluon radiation when an
energetic light parton travels through the ''brown muck''. The soft-overlap
contributions where the partonic momenta configuration is highly asymmetric are
disfavored, and the problematic end-point singularities and the double
countings are absent in this framework. A simple calculation with a natural
scale for the cutoff gives a plausible result for the $B\to\pi$ form factor.
