It seems like common sense but it’s so easy to rely on your day job income to pay for everything. I used to get paid a lot of money to go into work and sit at my desk for 8 hours a day and then go home. No manual labor required, no staying late hours(in my case at least) and a pretty low stress environment. I loved my job and without fail, every two weeks on the dot, a nice fat paycheck would show up in my bank account. All I had to do was show up at work every day and I was pretty much guaranteed to get paid.
Investing in coins and collectibles: Buffalo nickels and Spiderman comic books are good examples of coins and collectibles that can rise in value, and thus offer opportunity for passive income investors. You'll need to get up to speed on the value of any coin or collectible under consideration, but once you do so, you're on the way to price appreciation on a commodity you'll be paying a lower price to buy, and will garner a higher price when you sell.
Primary energy consumption of India is the third-largest after China and the US with 5.3% global share in the year 2015.[220] Coal and crude oil together account for 85% of the primary energy consumption of India. India's oil reserves meet 25% of the country's domestic oil demand.[209][221] As of April 2015, India's total proven crude oil reserves are 763.476 million metric tons, while gas reserves stood at 1,490 billion cubic metres (53 trillion cubic feet).[222] Oil and natural gas fields are located offshore at Bombay High, Krishna Godavari Basin and the Cauvery Delta, and onshore mainly in the states of Assam, Gujarat and Rajasthan. India is the fourth-largest consumer of oil and net oil imports were nearly ₹820,000 crore (US$110 billion) in 2014–15,[222] which had an adverse effect on the country's current account deficit. The petroleum industry in India mostly consists of public sector companies such as Oil and Natural Gas Corporation (ONGC), Hindustan Petroleum Corporation Limited (HPCL), Bharat Petroleum Corporation Limited (BPCL) and Indian Oil Corporation Limited (IOCL). There are some major private Indian companies in the oil sector such as Reliance Industries Limited (RIL) which operates the world's largest oil refining complex.[223]

Sonme months back, I heard the founder of in a TIE talk, where he shared that when they desperately needed some money in the starting years of their business, that time – one of the employee of an IT company put in Rs 1 lac in their business and within a year or two, he got back 20 lacs return through an exit option when they got funding later (it was something like this, if not exact)
An obvious example is over exposure to bank stocks, which have been excellent investments for over a century.  Though a foundation of most portfolios, bank stocks do involve more risk at certain stages of the economic cycle than many realise.  Being less exposed to bank shares in the last few months could have preserved some capital.  So, a more diversified approach can help mitigate some of these risks.