Social loafing is a phenomenon in which people intentionally do less towards a goal as part of a group than they do when working alone.
A number of researchers have examined this, measuring reductions in how much effort people expend as the size of the group increases. For groups of two, various studies have shown effort to be 82% to 93% of what individuals would do alone. Does this apply to the workload in marriages? I suspect it does, or at least there is a temptation to do less.
Another piece of this is the “matching of effort” – people who think they are doing more than their fair share will lower what they do to match what they perceive others doing. In marriage, this would mean the spouse who feels they do more than half might suddenly do less. If both spouses feel they do more than the other does, things could get messy.
My suggestion is to figure out how much is reasonable for you to do, and do it. If that’s more than half, should you really be doing more than half? If so, fine. If not, why do you feel you should do more than half? If what seems reasonable to you is less than half, why does it seem right? It may well be right, but be sure, and be sure your spouse feels the same way, or understands why you feel you can’t or shouldn’t do more at this time.