Every ICO have a mission to make profit for their project, for investor and company. But, not easy to find good and success ICO to make it profitable. There are some ICO is fail and maybe fake/scam.
Here are the reason for beginner to don't invest all assets for ICO
1. Every beginners is likely to want the ICO token directly distributed to their wallet before the end of ICO.
This is makes the token price is dump and makes the ICO will fail before that ICO complete. Because many people who join that ICO can't wait to sell their token before the price is listed.
2. Many beginners think that ICO price is same after the end of ICO or the exchange price listed
Some beginner don't know if the price is only for ICO price and don't know the real price is listing after that token listed on exchange.
3. Some beginners didn't fully check the ICO before they invest
Not every good ICO Project is good for invest, there are many ICO is fake/phising and not all real ICO will success after there token listed in Exchange. This is why before invest in ICO, we must check it by looking the ICO feature and mission, The ICO Team, Domain age of their website, Roadmap and their Whitepaper
That's my opinion why begginer mustn't invest all for ICO to save their assets. Sorry for my bad English because isn't my main language
Contributing money to ICOs gives no rights to the contributor, they only get a token which may or may not go up in value of a company that may or may not succeed in its goal.
Best to wait till you see some actual evidence of success before purchasing any token. My two cents on the matter.