Excellent question. It is easy to get too focused on volume for a particular session. As with everything you have to fight to avoid getting tunnel vision, to avoid getting too focused on any one aspect regardless of its rank in importance. The key to a stock moving higher is big money, i.e., institutional money, moving into it. Thus we look at weekly accumulation over the life of a base to see if there has been overall accumulation or distribution in the pattern. You want to see more up weeks on rising volume as that shows there are net buyers of the stock. Then if the volume dries up at the breakout point, you want to see volume surge into the stock to show that the big money is again at work bidding it higher.
Now there is also the situation where there has been strong volume leading up to a move and the move itself is not supported by the huge trade. Leading up to the move, however, volume has been strong, indicating a lot of action in the stock. If the accumulation is solid and the daily price/volume action is good (up on up days, down on down days fo rthe most part), that is enough as long as the day the stock moves is not completely without volume.
As we saw Monday, that can occur where there is a holiday or some other reason trade is not huge. If we still see solid trade for a lighter volume session on the heels of solid volume and solid price/volume action, we can move into a position even if the trade on that particular day is not blowout. We saw that on Monday with several stocks.
The key is to avoid a situation where there is no solid volume on good price/volume action either right before or at the actual break higher itself. That shows a lack of big money interest at a critical point, and those moves are more prone to failure.