The biggest mistakes developers make that leads to bad ending for many projects are
1. Huge Discounts
Many new projects are still making this mistake over and over again, huge discounts like 50% is insane and it always bother me how the hell the early buyers won't end up dumping since they have already see big profits.
2. Lack Of Solid Products and Ideas
Lack of working products and real use cases is why many investors are not taking new projects very seriously, no one would want to hold such tokens or coins for long, developers need to start working on how their project's token or coin will be very demanding throughout the globe
3. Bad Exchanges
Imagine new projects that make over millions of dollars in ico or ieo and end up listing on bad exchanges with no enough volume, what do they expect to happen?
When the developers keep making the same mistakes again and again then it is fair to ask ourselves if those are mistakes at all or if they know very well what they are doing, I say this because as we know if you give huge bonuses then those that bought their coins early do not really have a reason to hold their coins and they will sell them dumping the price, however developers are not thinking about the long term well being of their projects, they just want to obtain money now and if that means giving those bonuses then they will do it.
Which is why if I see any of those 3 things happening in a project I immediately lose any interest I may have in investing in that coin.