On the contrary I would say if you are newbie then investing in shitcoins is the biggest mistake you will make in hope of diversifying your portfolio because bitcoin is the only best option for you while those altcoins are pump dump scheme to make profits for the whales only.You can check on CMC how top-10 have changed instead of bitcoin which remains always at the top.The main reason behind it there's no utility for these altcoins so no long-term price surge but if you can trade it short term you can give it a shot but as a newbie stay away from it.
Altcoin is not an option for a newbie, it is less risky to start holding Bitcoin before gaining knowledge but one can not take such risk on altcoins, and in the best interest of your investment bitcoin should be taken as a long-term investment.
Don't hold Bitcoin for the short term unless your are using Bitcoin to carry out daily transactions, such as paying bills, but if you are looking to make your savings in bitcoin, you must be determined to hold for at least 5-6 months and one year respectively.