Linear careers differ from portfolio careers just like a tree trunk differs from a coppice

Linear careers are like single tree trunks. 
Portfolio careers branch out like a coppice.
CorporateNature Metaphor Series, No 122

1. Some careers are straight tree trunks:

Many career paths are stable and predictable. If you pursue a career in medicine, you know the steps you need to take: study for years and invest consistent effort in one direction to obtain a specialisation. 

2. Other careers are crooked trees:
The tree trunk of a linear career is not always straight, just as trees don't always grow perfectly straight. In fact, German philosopher Immanuel Kant said that "out of the crooked timber of humanity, no straight thing was ever made." If you change direction, e.g. move from finance to teaching, the sharp turn would result in a crooked tree in the forest of life. Also, there may be smaller career hiccups (e.g. gaps and sabbaticals) that create knots in the wood grain. Yet, the resulting trunk after 30 or 40 years is still a single massive block of wood.

3. Portfolio careers are shaped like a coppice:
Some people have portfolio careers: a diversified set of activities, such as consultancy, entrepreneurship, sitting on corporate boards, volunteering for charities. This model resembles a coppice. Coppicing is done by cutting down a tree to the ground, so that multiple shoots come out from the stump and grow into a bunch of (thinner) trees. Coppicing stimulates growth and increases the yield of harvested timber. By foregoing a linear career, you get a more interesting and diversified portfolio career which may result in a bigger timber harvest, i.e. higher income compared with a single salary job.

4. A "tree trunk" or a "coppice" career is mostly down to choice
Most trees can be coppiced: typically hazel, ash, willow, elm, beech, oak, chestnut. However, a small number of trees are not amenable to coppicing, for example birch. So it is of paramount importance for the "birches" among us to know that they should not pursue portfolio careers.

Coppice tree
(image source: Wikipedia)

Walking on lake ice is like navigating corporate culture: slippery and occasionally sinking

Clear ice is stronger than white non-transparent ice on a frozen lake; Transparent companies are safer to work for or work with than murky ones.

CorporateNature Metaphor Series, No 119

When walking on a frozen lake, you should step on the stronger clear ice and avoid the weaker white ice. Choosing the company to work for or work with has analogous parallels. 

1) CLEAR ICE: 

Companies with transparent employment practices are like clear ice.

Clear ice is formed when still water freezes directly. There are few air bubbles, which results in solid ice, so even though he surface is slippery, it is firm under your feet. Similarly, companies with transparent employment practices have fewer undefined “air pockets” in the corporate structure and provide a well-charted course for career development. The same metaphor also holds for dealing with or investing in companies. A “clear ice” company has transparent financing and is less likely to suddenly spring a hole and sink. 

2) WHITE ICE: 

Companies with “murky” nepotistic employment practices are like white ice.

White ice contains air bubbles and impurities which compromise the integrity of its structure and make it more fragile and unreliable to support your weight on your journey across the lake. In a similar way, a company with nepotistic employment practices ("air pockets") offers an uncertain future: you would not have a clear roadmap since career advancement is not entirely determined by performance. And when dealing with a "white ice" company as a supplier or a customer, you constantly have to be on the lookout for concealed financial information or quality-cutting practices.

Whether you are seeking employment or a corporate partnership, consider the risks of taking a step off the clear ice and onto the white ice on the frozen surface of the "corporate lake".

Frozen lake in Canada
(image source: Wikipedia)