My circumstances wont allow me to walk the complete camino. I wanted to start in France.. and finish from sarria to santiago. I am successfully finding ways to do that with the time i have available. This forum has been very helpful at finding those creative solutions. Its not conventional but its working so far.
There is not such a thing as 'the complete camino'. There are many, many different camino's (Camino Primitivo, Camino del Norte, Camino Invierno, Camino Baztan, Camino de Madrid, Via de la Plata, Camino Portugues and many more) and everybody can start where he/she decides.
Many people living in my country (the Netherlands) start at their front-door ... Other people with lack of time start (on the Camino Francés) from Burgos, Sahagún, León, Ponferrada, Sarria, depending how many days/weeks they have.
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@Tincatinker stated: if you travel from Pamplona to Sarria you will spend your spare time travelling by bus/train from A to B. And why? If you start in SJPdP you will meet other people, have nice chats while walking and during your dinner together. This is called your 'Camino family'.
Then you will leave them in 3/4 days, just for another stressful bus/train travel to Sarria, where you will be in another 'bubble' with different people.
If I were you and if I did not care about obtaining a Compostela, I'd walk as far as my time permits me to do so (and if possible I'd come back next year or so to continue where I stopped last time).
Or, if you want to receive a Compostela, I would start from León or Ponferrada to walk the last stretch of the Camino Francés.
Or: go to Porto and walk the Camino Portugues to Santiago de Compostela.
The whole idea of 'the complete Camino' may be developed since the movie 'The Way', but this is only a (romantized) story in a movie!
There have been Camino's for more than 1000 years, pilgrims came from all places in Europe to Santiago de Compostela, from North, South and East, and they all walked a true Camino!