Development of the SIZE Model (1999–2004)
The SIZE Basic Model is grounded in well-established psychological insights and combines approaches from depth and humanistic psychology with classical transactional analysis. Furthermore, it integrates bioenergetics as developed by Alexander Lowen and Ron Kurtz, as well as classical concepts of personality development.

Between 1999 and 2004, the Basic Model was developed by Hannes Sieber (Germany) and Fritz Zehetner (Austria). The name SIZE is derived from the initials of their last names: SI (Sieber) and ZE (Zehetner). In 2004, Sieber and Zehetner parted ways.

Continuation and International Protection of the Brand (since 2004)
Since 2004, Fritz Zehetner has continued to develop the SIZE PROZESS® model in ongoing collaboration with experts. His wife, Gabriele Zehetner, took on the primary role in economic and operational management. Together, they obtained European-wide trademark protection for the SIZE PROZESS® brand.

Today, Fritz Zehetner is regarded as an expert in personality diagnostics and individual development. In his roles as a developer and business consultant, he acts as a bridge between theory and practice. Zehetner draws upon his experience as a former successful executive in business, combining practical insights with solid theoretical knowledge to provide coaches, consultants, trainers, and leaders with practical, solution-oriented tools.

Zehetner is less of an academic researcher and more of a pragmatic developer. His goal is to translate psychological theories into easily understandable and applicable models for the everyday work of coaches and consultants.

Moving Away from Rigid Typologies Toward Systemic Thinking
Fritz Zehetner consciously breaks with the traditional, rigid typologies of the 1960s and 1970s and increasingly adopts a systemic approach in his work. He emphasizes that personality cannot be categorized into fixed types. Instead, the SIZE PROZESS® model views personality as an interplay of six dynamic personality styles that continuously interact with each other and with the environment. The flexibility and adaptability of these styles to different life situations and contexts are at the core of his approach. The model is designed to foster the individual potential of people and teams by focusing on clients' strengths, potentials, and psychological needs.

Integrative Approach: Theory for Practice
In his integrative approach, Zehetner combines various disciplines:

• Classical and systemic transactional analysis
• Systemic concepts
• Modern neuroscience

This creates a functional and widely applicable model, recognized and used throughout the coaching, consulting, and training landscape. A central goal for Zehetner is to promote self-reflection and personal development through his models.

Practical Focus as a Stated Goal
Rather than presenting theoretical concepts in isolation, Zehetner aims to translate psychological insights into comprehensible and practical formats. He manages to reduce complexity without losing essential content. Consequently, the SIZE PROZESS® model is appreciated not only in theory but also as a valuable tool for practical application—a model that clarifies personality structures and supports the realization of individual potential.