A T-shaped person is capable in many things and expert in, at least, one.
As opposed to an expert in one thing (I-shaped) or a “jack of all trades, master of none” generalist, a “t-shaped person” is an expert in at least one thing but also somewhat capable in many other things. Alternate phrases for “t-shaped” include, “multi-skilled”, “generalizing specialist”, “icicle-shaped”, “paint drip”, and “broken comb”.
T-shaped people is about adapting to varying demand.
Product delivery teams get asked to do a lot of different things, each of which require different skillsets.
We have two general ways to respond to this. The first is to adjust what gets scheduled to balance against what we can handle, aka demand-leveling.
The second approach is to make our response more adaptable through T-shaped people.
Use experts to clear bottlenecks.
Let’s imagine we have an incomplete task that is blocking overall progress due to dependencies. In this case, the best person to work on the blocking task is the person who can complete it the fastest. The word we assign to people who can complete a particular type of task the fastest is “expert”. Experts are most valuable to clear bottlenecks.
Use non-experts to free up expert time to clear bottlenecks.
Not every task requires an expert. Offloading non-expert tasks to non-experts frees up expert time to be available for bottlenecks. T-shaped people create more availability of non-experts for various tasks.
If non-experts can help with clearing bottlenecks, they should help.
Let’s say someone is an expert at a non-bottleneck task but can help out as a non-expert for a bottleneck task. What should be done? Even partial ability at a bottleneck is valuable. Being an expert on a non-bottleneck task is essentially wasting time. It has no impact on overall throughput. See Theory of Constraints.
T-shaped people means we can do more with the same number of people (or do the same with less people).
If people only know 1 skill, then, if developing your product requires n skills, you will need n people. If people know more than 1 skill, then you will need <n people.
T-shaped people help us communicate more effectively.
By learning each others’ skills, we also learn each others’ domain-specific language. This helps us communicate more effectively as we have more understanding of different perspectives.
T-shaped people is about embracing human adaptability.
A skill that you know well and find mundane might be very interesting and challenging to someone else who doesn’t know that skill. A skill they know well and find mundane might be very interesting and challenging to you. Cross-training to be more T-shaped enables this learning and growth mindset.
Beyond T-shaped
“Pi-shaped”, “M-shaped”, and “comb-shaped” metaphors extend T-shaped by indicating an increasing number of specialisations. I’m sceptical that the implied progression from T to Pi to M to Comb reflects how this actually works.
I also agree with Scott Ambler that “comb-shaped” doesn’t sound as cool as “T-shaped”. Whereas “T-shaped” describes a destination, his “generalizing specialist” phrase is trying to describe the journey.
Dave Rooney uses a metaphor of “icicle-shaped”, that is, people who pick up whatever skills they need when faced with a problem to solve. This matches more closely to how I actually operate.
Kent Beck is also unhappy with “T-shaped”, preferring a more exploratory, curiosity-driven style. He describes this as “paint drip”.
Jared Spool apparently uses a “broken comb” metaphor. I couldn’t find a direct reference but this is another article that describes it.
“E-shaped” and “X-shaped” metaphors don’t make any sense to me.
To learn more
If you want to learn more about this overall topic, I recommend reading chapter 6: Applying WIP Constraints in The Principles of Product Development Flow.
The earliest reference to T-shaped skills seems to be from 1978 in “Scientists Become Managers-The “T”-Shaped Man” by D.L. Johnston in IEEE Engineering Management Review
