Trend lines, "the steeper its the less reliable its"

in school of pipsology it stands "The STEEPER the trend line you draw, the less reliable it is going to be and the more likely it will break."
what does steep mean? i have tried google searching it but im still confused what a steep trend line is.
does steep mean more vertical or more horizontal?

I haven’t visited the school but its a general rule that if you draw a trend line that’s rising at x pips per day and then the trend accelerates to 2x pips per day, market participants are likely to start closing or reducing their older long positions. This tendency accelerates as the trend accelerates. Eventually this stops prices rising. However, that does not mean prices will start to fall.

ah okay so for example in a downtrend the more vertical the trend line is the less reliable its.
and in a uptrend the more vertical its the less reliable its. because both signals a strong move in one side which can just be a reaction to some news or something whatever.

Yes. An acceleration of a trend could be due to news or just latecomers jumping into the price movement. But a pause in price rises becomes increasingly probable. This can become, in order of probability -
a short pull-back, or
a prolonged congestion zone, or
an even longer range, or
a reversal.

Continuation of the original trend is the most probable outcome from a pull-back or congestion zone. A range could go either way, while a reversal is what it says. But I don’t like the word “break” in the original post. Its very possible for price to drop through the trend-line but the underlying trend remains. In any case, your trend-line isn’t necessarily everyone else’s trend-line, its a subjective construct, so it has to be good to see some confirmation a trend has definitely ended before you abandon your positions or this chart.

I think tommor is dead on as usual. I use trend lines but only to supplement my horizontal s/r lines because i think horizontal lines are stronger. Just my 2 cents