Being steady in our daily duties is heroic, especially today.
If we can't even do many small acts perfectly, and I assume it's a struggle for most of us, how can we imagine we will be victorious in one big act? If we can't withstand fatigue, pain, want, or discomfort in small ways now, how can we imagine we will withstand death? Actual death. Not the painless, glorious, slightly prideful, slightly biased and unrealistic death in one's imagination as a martyr, but to actually be murdered.
When Bp Williamson speaks of potential martyrdom, that translates in my mind as a call to continue striving for sanctification in our daily duties until the day if/when God decides otherwise.