Recall that lightness consists of two primary elements: a sense of unfettered choice and a disinclination to treat events and circumstances with excessive seriousness. Making and pursuing any decision of significance, therefore, impedes lightness on both accounts. Though having made a decision we remain free to change it, the costs of such a change are usually considerably higher than having made a different decision initially. For what is a decision but a commitment that has, at minimum, opportunity cost, and usually at least an emotional "restocking fee," if not actual out-of-pocket costs in time, money, and effort? Thus we feel impelled to follow through on a decision, at least to a point; our options then seem more limited, and we are not as light as before.
Often, though not always, a significant decision is also accompanied by efforts and focus directed toward obtaining a successful outcome related to the decision. Combined with the experiential reduction of choice, such efforts take on an air of heaviness, an importance that may give rise to anxiety, fear of failure, inattention to everyday pleasures, and the like. One would have to be preternaturally blithe to live to adulthood without experiencing this effect.
The obvious way to avoid the situation is simply to eschew decisions. However, though it may be wise to consider whether a commitment is necessary in each particular case, as a universal this approach has numerous flaws. First and foremost, the lack of a decision is a decision of another kind. There are many enjoyments - monogamous love, or a home, for example - in which the commitment is central to the experience. Second, and overlapping, there is an existential discomfort, "unbearable lightness," as it is sometimes called, to living every day with unrestricted choice, with no guidance from precedent. Finally, it is very common in the absence of a decision for fortune to decide for us, and only rarely does a roll of the dice expand rather than compress our options.
In cases where we have appropriately made a choice, we can confront the challenge to our lightness by consciously managing it. This initially seems contrary to the spirit of lightness: if it is consciously directed, it hardly seems carefree. But recall that this is prescribed in the aftermath of a major decision, not as an unrelenting burden. It is a way to retain, as much as possible, a light demeanor during periods when focus and effort increase and choice has evidently decreased.
The mechanics of such management are straightforward enough. Circumscribing the times and places for focus and effort enables one to more fully enjoy everyday pleasures outside those bounds. In particular, the mental state associated with effort has a tendency to engulf all of one's activities, and this overflow must be avoided. Maintaining perspective on the worst case and likely scenarios usually reduces tension associated with the possibility of undesirable outcomes. Keeping in mind the original reasons for the decision, particularly the expanded choices and experiential opportunities that were its object, mitigates the short-term feeling of loss of autonomy. Awareness of countenance can curtail unintended incivilities that might instigate a spiral of despair.
It may seem that this management is an additional onus, above and beyond the effort already required to make good on the decision itself. But this is an error arising from separation of an element that is actually part and parcel of a decision, if one wishes to live with lightness. When making a decision, and evaluating its benefits and costs, the effort of consciously managing lightness through the most challenging period is an essential part of the decision, along with whatever other efforts are anticipated. Indeed, since this is part of any major decision, it could very well be the first rather than the last thing to consider.