  We consider universal aspects of a holographic Schwinger effect in general
backgrounds with an external homogeneous electric field. The argument is based
on the potential analysis developed in our previous work. Under some
conditions, there always exists a critical electric field, above which the
potential barrier vanishes and the system becomes unstable catastrophically.
The critical value agrees with the one obtained from the Dirac-Born-Infeld
action. For general confining backgrounds, we show that the Schwinger effect
does not occur when the electric field is weaker than the confining string
tension.
