T-shaped refers to someone who possesses deep skills along with a broad base of shallow ones. The concept splits the T letter into two bars - horizontal and vertical.
T-shaped people have vertical (specialized) skills but also horizontal (general) knowledge in other disciplines. An I-shaped person is one who is a functional expert whose functional expertise being represented by the vertical stroke in the letter I. The horizontal stroke of the T representing cross-functional awareness and understanding.
Vertical bar:
The vertical bar comprises a bundle of deep knowledge in a single area to facilitate the creative process. It means that being a niche professional (designer, architect, social scientist, business specialist, mechanical engineer, etc.) combined with related skills and experience makes your I-bar longer. Although they are highly valuable, I-shaped people are likely to fail in workplaces that are associated with a high level of collaborative labor.
Horizontal bar:
The horizontal bar includes a range of skills in the areas unrelated to the primary one. Nevertheless, the breadth of these skills allows you to cooperate with representatives of other fields and share a common language with them. Those who tend to have a wide horizontal bar not supported by discernible specialties are known as dash-shaped people or generalists.
From Software perspective:
The vertical bar represents depth in a single technical discipline, and the horizontal bar represents the ability to apply knowledge across disciplines and to work with others.
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