When I look at the market in the chart below, I see three things:

A. The market has continued its rise as of late

B. It is doing so on overbought and negative-trending momentum

C. It has done so on weakening volume.

In a healthy, northward trending market, we would see momentum indicators — such as the moving-average convergence/divergence (MACD) at "A" — trending up along with the market. Instead what we see here is negative divergence with momentum pointing southward, against the trend. This unfavorable signal against the grain of prevailing market prices indicates probable near-term trouble for the market.

Additionally, in a strong market, we would see robust volume accompanying the up-trend. Instead, what we see here is a Price Volume Oscillator (at "C") telling us that, from February through early April, volume actually receded while the market forged ahead. It is important to  avoid confusing this action as being  resilient. Again, stable volume that tags along with a trend indicates strength of the trend in place, and observing the chart above, it seems to me that momentum is shifting negative all while volume is starting to pick up some steam.

Human beings suffer from a serious case of recency bias, which results in investors quickly forgetting the pain once felt when markets drop. It took almost two years (from 2007-2009) for the market to ransack investors of more than 50% of their wealth. In 2008, there were exactly the same number of positive trading days as there were negative ones, but still the market fell 37%. People kept saying, "The bottom  has to be behind us at this point," but it wasn't.