Investment Strategy - Looking for sustainable growth

In books, we always find that the company can grow infinitely. That is why we always think that equity is always a better asset class to overcome the long term inflation. But in real case, we cannot avoid the underlying business risk the company has, especially when the company is in the competition.

Building a diversified portfolio maybe is a good idea, but naively diversify the portfolio into many difference piece of asset classes equally would make you look like like an idiot, even though it may bring the benefit of diversification.

Timing the market could be another good idea too, but empirical research showed that it may not be a suitable investent strategy to everyone, as sost of the time we are affected by the market. A "cut profit" or "cut loss" strategy could lead to excessive trading, and we may lost opportunity cost due to over trading.

To look for sustainable growth, we must develope a circle of competence, in the sectors that we are looking at. For example, I cannot apply the view of property sector in investing in commodities sector, as the correlation between them is little.

I have been following offshore & marine industry for a few months. I know that current oil & gas industry is in another new circle, as the equipments are aging and we would require a better and more efficient and safe rigs in the oil & gas industry. With the oil price still stands at 80USD and above, we can foresee that there will be more upcoming projects to build more rigs / ships to deliver the oil. However, I do not really know that how long is this circle and when will it end and the impact of oil prices to the industry. I can apply momentum investing strategy by buying in a company that is having a lot of contracts (large order book), but I have the worry that the order book value may drop, after the peak period ends.

So what could be the "sustainable growth" that I am looking for?

Consumer sectors, utility sectors and healthcare sectors are the industry that I can think of. However, this is only my own opinion. Finding a distressed company would be my another homework. Of course, above are all in theory. I will let you know the result after I have the result later.