From what I can understand (which I will freely admit is somewhat limited, and biased), it seems to me that the root of the problem is that we let the very wealthy soak up all the economic gains due to productivity over the course of a few decades, while also letting those with more money have more influence over our politics (thus meaning that they had the means to ensure their gains would be locked in, rather than redistributed for the benefit of those who actually created them—ie, the workers).

Until we can collectively recognize this and address the staggering socioeconomic inequality in our society, we're going to keep seeing the economy limp and sputter frequently. A healthy economy needs its working class—the vast majority of people in it—to overall have healthy economic situations, enough for at least some disposable income on a regular basis on top of being able to comfortably pay for basic necessities and save a bit for the future. Ideally, it needs that to be the minimum condition, so that everyone in the economy has some genuine discretionary spending capability.